First time I took my R-25 in .308 it had cycling issues the first mag.
Then I gave the bolt carrier a liberal squirt of oil, tried again and it ran fine.
They are tight when brand new, they do have a little break-in period it seems.

The force it takes to rotate the bolt head in the carrier (when rifle disassembled) is night and day difference between brand new and a few hundred rounds.

I have only run the DPMS 10 rd mags so far, have others but never bothered using them.